This invention relates to a method for transferring an epitaxy layer, and more particularly to a method for transferring a GaN (gallium nitride) thin film obtained by epitaxy lateral overgrowth (ELO or ELOG) method.
Generally, various electronic or optoelectronic devices, such as light emitting diode and semiconductor laser diode, are mainly fabricated from semiconductor material which is grown by the epitaxy growth method. In this fabrication method, an epitaxial substrate is needed to be deposited by the material through its growth. And, lattice constants of the epitaxial substrate and the semiconductor material should match to each other for forming high quality semiconductor material with lower defect so as to obtain the optoelectronic and electronic devices with high performance and efficiency. However, the limited epitaxial substrate restricts the application scope and performance of the semiconductor material which is grown by the epitaxy growth method. Thus, these epitaxial material and structure are usually needed to be separated from the original epitaxial substrate and then be transferred to another substrate having different material properties which dose not allow the epitaxy material to grow thereon or can""t get high quality epitaxial crystal, to increase the application.
Take GaN as an example. Recently, because GaN is difficult to grow bulk material, there dose not exist a GaN epitaxial substrate and GaN needs to epitaxy on the substrate made by other material. But, the epitaxial substrate that are usually used for growing GaN actually has some properties which are harmful to the device operation or commercial large-quantity production, such as insulation, hard, low thermal conductivity . . . etc., and all these cause the limitation of usages or efficiency of GaN. Consequently, the wafer bonding technology has been cooperated with substrate removing or substrate transferring to transfer the GaN epitaxy layer to another substrate for increasing the application or decreasing the manufacturing cost thereof.
Presently, the technologies for separating the GaN from the substrate include the laser lift off method and the smart cut method. But, both of them have limitations and disadvantages in applications. Generally, the laser lift off method is restricted by the smaller spot size of the laser beam and only can be used to separate a small portion of the GaN epitaxial layer at a time. Except the disadvantage described above, another drawback with using this method is that the energy of the laser beam is not easy to spread averagely and will then cause different decomposition rate and heat accumulation in different portions of the GaN epitaxy layer. Because it is hard to precisely control the heat transfer and decomposition at the GaN/substrate interface, partial surface of GaN layer therefore will become rough after being separated by this method. Furthermore, because of a thermal shock in the material, the quality of the GaN layer will be reduced, even more the GaN layer will be unusable. Consequently, the expensive laser equipment with smaller production efficiency is inappropriate for large-quantity production and also not suitable for saving the cost.
As to the smart cut method, this method implants ions into the epitaxy layers before wafer bonding being progressed. Thus, the epitaxy layers are heated to vaporize ions to provide pressure for separating. However, the ion implantation process will destroy the crystal structure of the epitaxial layer, and the defect density which influences the device performance and the material quality will also be increased. Consequently, this method is not suitable to transfer semiconductor epitaxy layer for commercial purpose, either.
In addition, both of the methods have some other disadvantages that they are not appropriate for transferring the epitaxial layer in large area, the transferred epitaxial layer owns low quality, the epitaxial substrate can not be recycled, and the cost of the manufacturing process is much higher.
Because of the problems described above, the applicant keeps on carving unflaggingly to develop a xe2x80x9cmethod for transferring epitaxy layerxe2x80x9d through wholehearted experience and research.
It is an object of the present invention to provide a method for transferring an epitaxy layer obtained by a lateral overgrowth method to a needed substrate without hurting the original substrate and the epitaxy lateral overgrowth layer.
It is another object of the present invention to transfer a GaN epitaxy layer obtained by the lateral overgrowth method to another selectable substrate for obtaining a high quality GaN with a selectable substrate to providing different usages therefor.
In accordance with an aspect of the present invention, a method for transferring an epitaxy layer includes steps of (a) providing a first substrate, (b) forming a first epitaxy layer on the first substrate, (c) forming a masking layer having at least a pattern on the first epitaxy layer, (d) forming a second epitaxy layer on the masking layer, (e) bonding a second substrate to the second epitaxy layer, and (f) removing the masking layer and separating the second epitaxy layer from the first epitaxy layer, thereby the second epitaxy layer being transferred to the second substrate.
Preferably, the first substrate is one selected from a group consisting of gallium arsenide, sapphire, silicon carbide, and silicon.
Preferably, the first epitaxy layer includes a low-temperature buffer layer (LT-Buffer Layer) and a high-temperature epitaxy layer.
Preferably, the LT-Buffer Layer is one selected from a group consisting of gallium nitride, aluminum nitride, and gallium aluminum nitride.
Preferably, the LT-Buffer layer is formed at a temperature ranged from 600 to 700xc2x0 C. and has a thickness ranged from 200 to 500 xc3x85.
Preferably, the high-temperature epitaxy layer includes gallium nitride.
Preferably, the high-temperature layer is formed at a temperature ranged from 1000 to 1100xc2x0 C. and has a thickness about 1.5 xcexcm.
Preferably, the masking layer is one of a metal and a ceramic.
Preferably, the metal includes tungsten.
Preferably, the ceramic includes one of silicon nitride and silica.
Preferably, at least a pattern includes one of dot opening and line opening.
Preferably, the step (d) further includes a step (d1) of forming a bonding medium layer on the second epitaxy layer.
Preferably, the bonding medium layer is one selected from a group consisting of palladium (Pd), titanium (Ti), indium (In), nickel (Ni), gold (Au), and a mixture thereof.
Preferably, the second epitaxy layer is an epitaxy lateral overgrowth layer.
Preferably, the second epitaxy layer includes gallium nitride (GaN).
Preferably, the step (e) further comprises a step (e1) of forming a bonding medium layer on the second substrate.
Preferably, the bonding medium layer is one selected from a group consisting of palladium (Pd), titanium (Ti), indium (In), nickel (Ni), gold (Au), and a mixture thereof.
Preferably, the second substrate includes silicon.
Preferably, the step (e) is implemented by a wafer bonding process.
Preferably, the wafer bonding process further includes a thermal annealing process.
Preferably, the step (f) is executed by a wet etching.
In accordance with another aspect of the present invention, a method for transferring an epitaxy layer includes steps of (a) providing a first substrate, (b) forming a first epitaxy layer on the first substrate, (c) forming a masking layer on the first epitaxy layer and then etching the masking layer to form at least a pattern, (d) forming a second epitaxy layer on the masking layer, (e) removing the masking layer, and (f) bonding a second substrate to the second epitaxy layer and separating the second epitaxy layer from the first epitaxy layer so as to obtain the second substrate with the second epitaxy layer.
Preferably, the first epitaxy layer includes a low-temperature buffer layer (LT-Buffer Layer) and a high-temperature epitaxy layer.
Preferably, the step (d) further (d1) of forming a bonding medium layer on the second epitaxy layer.
Preferably, the second epitaxy layer is an epitaxy lateral overgrowth layer.
Preferably, the step (e) is executed by a wet etching.
Preferably, the step (f) further comprises a step (f1) of forming a bonding medium layer on the second substrate.
Preferably, the step (f) is implemented by a wafer bonding process.
Preferably, the wafer bonding process further includes a thermal annealing process.
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed descriptions and accompanying drawings, in which: